The answer, it seems, is because Apple recently defected from traditional quartz-based clocks in its phones in favor of clocks that are also made of MEMS silicon. Given that clocks are the most critical device in any computer and are necessary to make the CPU function, their disruption with helium atoms is enough to crash the device.
In this case, the leaking helium from the MRI machine infiltrated the iPhones like a “tiny grain of sand” and caused the MEMS clocks to go haywire.
MEMS oscillators incorporate MEMS resonators, which are microelectromechanical structures that define stable frequencies. MEMS clock generators are MEMS timing devices with multiple outputs for systems that need more than a single reference frequency. MEMS oscillators are a valid alternative to older, more established quartz crystal oscillators, offering better resilience against vibration and mechanical shock, and reliability with respect to temperature variation.
So the helium causes physical interference by leaking into the housing?
Yup. Helium is such a tiny thing it can diffuse through almost anything, and in MEMS oscillators which are supposed to be at a rock solid 32kHz, causes variance in the frequency eventually just "gumming" it up entirely and causing it to stop working.
...Yet both Android and Apple phones use MEMS silicon for their devices, so why were only Apple phones affected?
The answer, it seems, is because Apple recently defected from traditional quartz-based clocks in its phones in favor of clocks that are also made of MEMS silicon.
So, they ask the question of why iPhones are the only ones affected if androids also went to MEMS, then answer it by saying that apple went to MEMS. Are they saying that the clocks in Androids still use quartz, but iPhones use MEMS clocks, even though they both use general MEMS silicon?
Are they saying that the clocks in Androids still use quartz, but iPhones use MEMS clocks, even though they both use general MEMS silicon?
Correct. MEMS technology is used in the accelerometers and gyros in the inertial measurement units (IMUs) that are in pretty much every smartphone. Apple decided to switch to using MEMS clocks, probably because it means that they can reduce part count slightly as it would mean that they can incorporate them on the same chip as the CPU or the like.
Helium doesn't just kill apple devices, It kills anything with a MEMS oscillator. Helium atoms are so small that it's impossible to make a seal that completely blocks them.
Well that's not true. It's just a real bitch. As a welder, helium leak check is about the toughest damn QC to pass. Most welding QC has some reasonable margin for error during inspection, but the damn helium doesn't care. You can have a beautiful weld with a tiny imperfection at the start or end and it'll piss helium just as badly as an entirely scuffed bead.
If you are in a position where you can dump random gases into the air supply to the degree it impacts these devices then they are likely compromised in other ways as well.
Can't speak for MEMS specifically, but it absolutely can make chips shut down whole instruments by changing their properties. It intercalates slower, but has much the same effect once it's in there.